Flame-retardant compounds combining polypropylene and various inorganic fillers are known in the prior art. However, these prior art filled polypropylene compounds generally suffer from one or more serious disadvantages making them less than entirely suitable for their intended purpose.
One commercially available polypropylene compound has a formula that includes 27 wt% chlorinated paraffin and 10 wt% antimony oxide. Another polypropylene compound, disclosed in U.S. Pat. No. 4,234,469, comprises an inorganic filler (either talc, kaolinite, sericite, silica or diatomaceous earth), antimony oxide and an organic halide flame-retarder (decabromodiphenyl ether, dodecachlorododecahydrodimethanobenzocyclooctene, or mixtures thereof). Polypropylene componds containing chlorinated paraffin or other organic halides generally possess satisfactory resistance to high temperature conditions. However, these compounds are difficult and expensive to mold because it is not practical to avoid the formation of HCl or HBr under commercial operating conditions. Consequently, the molds must be coated with gold or other expensive acid-resistant metal.
It is a principal object of the present invention to provide a flame-retardant polypropylene compound containing an inorganic filler and no organic halide compounds.
It is a related object of the invention to provide a flame-retardant polypropylene compound that is filled with alumina hydrate and possesses better physical properties and improved processing characteristics compared with prior art alumina hydrate filled polypropylene compounds.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and claims.